This invention is directed primarily toward providing an improved cutting system for use in tape laying machines. Such tape laying machines are known in the art and are used for manufacturing aircraft structures from composite tape materials. An example of a type of tape laying machine into which the method and apparatus of the present invention could advantageously be incorporated is the machine developed by the Vought Corporation and described in the Jan. 24, 1983 issue of Design News, in the article on pages 136 and 137 entitled "CNC Machine Slashes Laminated Composite Cost".
The composite tape materials used in conjunction with automatic tape laying machines for manufacturing aircraft structures are normally provided in double layer form. The top layer is the composite material itself, and the bottom layer is backing paper. The purposes of the backing paper include preventing the sticking together of layers of the composite material in rolls of the tape, preventing resin build-up on machine parts, and providing a continuous strip for transporting the tape from the supply reel. Because of the last named purpose, it is of course necessary to avoid cutting through the paper when the top layer of composite tape material is cut.
A problem that is encountered with known methods for cutting the top layer is that a few fibers at the lateral edges of the composite material sometimes escape being cut. One cause of this problem is the tendency of some cutters to push or pull these fibers off the backing paper. Another cause is inherent in the nature of the composite material and the manner in which the tape is manufactured. The composite material includes numerous fibers in a bonding medium. The double-layer tape is manufactured in wide sheets that are cut longitudinally to form double-layer tapes of a desired width. When the longitudinal cuts are made, some of the composite fibers are pushed down by the longitudinal cutter and end up adjacent to the lateral edge, rather than the top surface, of the backing tape. The cutting apparatus of conventional tape laying machines misses these fibers when making lateral cuts of the composite material.
The undesirability of such missed fibers should be obvious. If they are not detected in time, they will be pulled along with the backing paper as the tape laying head moves into position to lay the next course. This ruins the course of composite material that has just been laid. The machine has to be stopped and the damaged composite material must be removed before the tape laying process can be resumed. This results in considerable additional expense due to increased personnel costs, wasteful downtime of an expensive tape laying machine, and waste of the damaged composite material which must be discarded. Even if the missed fibers are detected in time, the cost of the operation is still significantly increased. The machine must be stopped to allow the missed fibers to be cut by hand. Again valuable machine time is lost and personnel costs are increased. The machine operator has idle time and at least one extra worker is required just to watch for missed fibers, shut down the machine as necessary, and hand cut missed fibers. In addition to the increased cost, the hand cutting process has the added disadvantage of being relatively imprecise, resulting in a lessening of the quality of the finished composite structure.
The primary object of the present invention is to solve the problem of missed fibers to thereby decrease the cost of the tape laying operation and improve the quality of the finished product.
The following U.S. Pat. Nos. each disclose apparatus for cutting and/or processing strip or sheet material:
349,388, granted Sept. 21, 1886, to F. A. Fowler; PA1 2,158,790, granted May 16, 1939, to H. J. Arthur; PA1 2,382,406, granted Aug. 14, 1945, to R. E. Engberg; PA1 2,637,394, granted May 5, 1953, to M. J. Fey; PA1 3,435,717, granted Apr. 1, 1969, to J. K. Macomber; PA1 3,558,109, granted Jan. 26, 1971, to M. Sofue; PA1 3,732,769, granted May 15, 1973, to J. Loersch; PA1 3,877,333, granted Apr. 15, 1975, to E. A. E. Illingworth et al; PA1 4,215,606, granted Aug. 5, 1980, to J. P. Britt; and PA1 4,354,408, granted Oct. 19, 1982, to C. R. Carte.
Macomber U.S. Pat. No. 3,435,717 and Carte U.S. Pat. No. 4,354,408 each discloses apparatus that includes a scissor-type cutter. Sofue U.S. Pat. No. 3,558,109 does not disclose any cutter. The remaining seven patents each discloses a guillotine or punch-type cutter. Except for Sofue U.S. Pat. No. 3,558,109, which does not disclose any cutting apparatus or procedure, each of the ten above-listed patents discloses cutting completely through the sheet material being processed.
In the apparatus of each of the ten above-listed patents, the sheet material being processed is bowed at some point during the processing. In Arthur U.S. Pat. No. 2,158,790, Engberg U.S. Pat. No. 2,382,406 and Carte U.S. Pat. No. 4,354,408 the bowing of the material is carried out for the purpose of stiffening the material and holding it in position to be easily grasped. In Fey U.S. Pat. No. 2,637,394, Sofue U.S. Pat. No. 3,558,109, and Loersch U.S. Pat. No. 3,732,769, the material is bowed to stiffen it in order to maintain a fixed length between two points (Fey), keep the material in a stable position for processing (Sofue), or keep the material in a stable position for cutting (Loersch). In Fowler U.S. Pat. No. 349,388 the purpose of bending the edges of the material is to bevel the edges. In Macomber U.S. Pat. No. 3,435,717, the purposes of bowing the material include engaging the feed means, registering a precut with the cutting means, and strengthening and coercing the material longitudinally. Illingworth et al U.S. Pat. No. 3,877,333 bow the material in order to advance the trailing edge toward the leading edge. In the Britt U.S. Pat. No. 4,215,606 apparatus, the material is bowed in order to form a break or cut across the lateral center of the material without stretching the connecting webs between the pieces of material, to control the length of the break, and to eliminate waste of the material.
The above patents and the prior art that is discussed and/or cited therein should be studied for the purpose of putting the present invention into proper perspective relative to the prior art.